1. Field of the Invention
This invention relates to an image recording medium on which an image can be recorded as a latent image and a method of manufacturing the image recording medium.
2. Description of the Related Art
In order to reduce irradiation dose to the patients and/or to improve diagnostic performance of the X-ray image in a medical radiography, there have been proposed various systems in which a photoconductive body sensitive to X-rays is used as an image recording medium, and an electrostatic latent image formed on the photoconductive body upon exposure to X-rays is read out. For example, see U.S. Pat. Nos. 4,176,275, 5,268,569, 5,354,982, and 4,535,468, xe2x80x9c23027 Method and Device for recording and transducing an electromagnetic energy patternxe2x80x9d; Research Disclosure Jun. 1983, Japanese Unexamined Patent Publication No. 9(1997)-5906, U.S. Pat. No. 4,961,209, and xe2x80x9cX-ray imaging using amorphous seleniumxe2x80x9d; Med Phys. 22(12).
For example, the image recording medium disclosed in U.S. Pat. No. 4,535,468 comprises a conductive substrate (which functions as a recording light side electrode layer) which is formed of, for instance, a relatively thick (e.g., 2 mm) aluminum plate and is permeable to recording light (an electromagnetic wave), and a recording photoconductive layer which is formed of a photoconductive material containing a-Se (amorphous selenium) as a major component and is 100 to 500 xcexcm in thickness, an intermediate layer (trapping layer) 0.01 to 10.0 xcexcm thick which is formed of, for instance, AsS4, As2S3 and/or As2Se3 and in which an electric charge of a polarity of latent image generated in the recording photoconductive layer gets trapped and accumulates, a reading photoconductive layer which is formed of a photoconductive material containing a-Se as a major component and is 5 to 100 xcexcm in thickness and a reading light side electrode layer which is formed of, for instance, Au or ITO (indium tin oxide) 100 nm thick and is permeable to reading light (an electromagnetic wave) which are formed on the conductive substrate in this order. There are further disclosed that it is preferred that the reading light side electrode layer be used as the positive electrode layer from the viewpoint of better use of mobility of positive holes and that deterioration in S/N ratio due to direct injection of an electric charge from the electrode layer can be prevented by providing a blocking layer of organic material between the reading light side electrode layer and the reading photoconductive layer. That is, the recording medium is a multi-layered recording medium which is formed of a plurality of layers of photoconductive material containing a-Se as a major component and is high in dark resistance and response speed to reading.
In order to increase the S/N ratio and to effect reading simultaneously at a plurality of places (normally arranged in the main scanning direction) to shorten the reading time, the reading light side electrode is sometimes shaped into a stripe electrode comprising a plurality of line electrodes arranged at intervals equal to the pixel pitch. See, for instance, Japanese Unexamined Patent Publication No. 10(1998)-232824. However it is difficult to form a stripe electrode layer on the reading photoconductive layer of the recording medium disclosed in the aforesaid U.S. Pat. No. 4,535,468. This is because the stripe electrode layer is formed by photo-etching a solid electrode layer and a-Se in the reading photoconductive layer deteriorates in its properties under a high temperature (e.g., 200xc2x0 C.) to which the reading photoconductive layer is subjected during, for instance, baking photoresist.
Further, alkali developer used for developing the photoresist emits harmful gas when brought into contact with the photoresist, and removal of the harmful gas complicates the manufacturing procedure and adds to the cost.
This applicant has proposed, in Japanese Unexamined Patent Publication No. 10(1998)-232824, an image recording medium (an electrostatic recording medium) comprising a recording light side electrode layer which is formed of SnO2 (nesa film) and is permeable to recording light (radiation), a recording photoconductive layer which is formed of a photoconductive material containing a-Se as a major component and is 50 to 1000 xcexcm in thickness, a charge transfer layer which is formed of, for instance, a-Se doped with 10 to 200 ppm of organic material or Cl and forms a charge accumulating portion for accumulating an electric charge of a polarity of latent image generated in the recording photoconductive layer on an interface between the recording photoconductive layer and the charge transfer layer, a reading photoconductive layer which is formed of a photoconductive material containing a-Se as a major component and a reading light side electrode layer which is permeable to reading light which are superposed one on another in this order.
In the specification of Japanese Unexamined Patent Publication No. 10(1998)-232824, there is no clear disclosure as for from which side the layers are formed, that is, whether the recording light side electrode layer is formed first and the reading light side electrode layer is formed last, or the reading light side electrode layer is formed first and the recording light side electrode layer is formed last. This means that the layers may be formed in whichever order. However, in the specification, there is proposed to use a conductive material layer such as a nesa film formed on a transparent glass plate (support) as the reading light side electrode layer and to use the reading light side electrode layer as the positive electrode layer. There is further proposed to form the reading light side electrode layer, by use of the semiconductor forming technique, as a stripe electrode layer or a comb electrode layer comprising a plurality of comb teeth electrodes arranged at intervals equal to the pixel pitch. In this case, the stripe electrode layer is first formed on a transparent glass substrate by photo-etching or the like and then the reading photoconductive layer to the recording light side electrode layer are formed on the reading light side electrode layer. Though not clearly shown in the specification, it is easy for a person with ordinary skill in the art to come up with the idea of setting the pixel pitch to 50 to 200 xcexcm since it is important in the medical radiography to obtain a high S/N ratio with a high sharpness.
As in the aforesaid U.S. Pat. No. 4,535,468, we have proposed in the aforesaid Japanese Unexamined Patent Publication No. 10(1998)-232824 to prevent deterioration in S/N ratio due to direct injection of a positive electric charge on the reading light side electrode layer by providing a blocking layer about 500 xc3x85 thick of inorganic material such as CeO2 between the reading light side electrode layer and the reading photoconductive layer.
We have further studied the image recording medium proposed in our Japanese Unexamined Patent Publication No. 10(1998)-232824 and have found the following points.
1) A method of forming the stripe electrode layer in which a relatively thin (e.g., 50 to 200 nm) ITO film is first formed on a transparent glass substrate and the ITO film is shaped into a stripe electrode layer by photo-etching is suitable for forming a fine stripe pattern at low cost.
2) By forming the recording photoconductive layer of an a-Se layer 50 to 1000 xcexcm thick, a higher dark resistance is obtained.
3) As the charge transfer layer, a laminated positive hole transfer layer, formed by a first positive hole transfer layer 0.1 to 1 xcexcm thick which is of organic material and accumulates electrons to form a charge accumulating portion and a second positive hole transfer layer 5 to 30 xcexcm thick which is formed of a-Se doped with 10 to 200 ppm of Cl, transfers positive holes at high speed and is less in positive hole traps, is advantageous from the viewpoint of afterimage and response speed to reading.
4) To form the reading photoconductive layer of an a-Se layer 0.05 to 0.5 xcexcm thick is advantageous in obtaining a high dark resistance.
5) When the charge transfer layer is in the form of a laminated positive hole transfer layer comprising a first charge transfer layer 0.1 to 1 xcexcm thick which is of PVK, TPD or the like and a second charge transfer layer 5 to 30 xcexcm thick which is formed of a-Se doped with 10 to 200 ppm of Cl, the first charge transfer layer comes to exhibit high resistance to the electric charge of the latent image polarity (the polarity of latent image) while the second charge transfer layer comes to transfer the electric charge of the transfer polarity (the electric charge of the polarity to be transferred) at high speed, which is advantageous from the viewpoint of afterimage and response speed to reading. However, when the second charge transfer layer is replaced by an a-Se layer 5 to 30 xcexcm thick and the a-Se layer is caused to double the second charge transfer layer and the reading photoconductive layer, a relatively excellent image recording medium can be manufactured with the manufacturing procedure simplified.
That is, the image recording medium proposed in our Japanese Unexamined Patent Publication No. 10(1998)-232824 is an excellent multi-layered recording medium which is high in dark resistance and response speed to reading, and is preferably formed of a plurality of layers of photoconductive material containing a-Se as a major component.
As is well known, in an a-Se film, crystallization progresses with time, which can give rise to a so-called bulk crystallization problem that especially the dark resistance deteriorates. The bulk crystallization significantly occurs when the a-Se film is of non-doped or pure a-Se and progresses at higher speed as the temperature is higher. Accordingly, the aforesaid image recording medium which comprises many layers of non-doped a-Se is severely limited in working temperature and service life.
Further, it has been well known that interfacial crystallization progresses on an interface between an a-Se film and another material during the step of depositing films. For example, when the recording light side electrode layer is deposited on the recoding photoconductive layer, the interfacial crystallization is apt to progress on the interface between the recording photoconductive layer and the recording light side electrode layer, which causes an electric charge to be directly injected into the recording photoconductive layer from the recording light side electrode layer during recording (where a high electric voltage is applied), which deteriorates the S/N ratio. When the electrode layer is of a transparent oxide film, especially an ITO film, the interfacial crystallization markedly progresses and deterioration in S/N ratio is significant.
In the image recording medium described above, a latent image is recorded by accumulating in the charge accumulating portion the electric charge of the latent image polarity generated in the recording photoconductive layer upon exposure to a recording electromagnetic wave passing through an object, and reading is carried out by coupling of charged pairs, generated in the reading photoconductive layer upon exposure to a reading electromagnetic wave passing through the reading light side electrode layer, with the electric charge of the latent image polarity in the charge accumulating portion.
The charged pair generating efficiency of the recording photoconductive layer is proportional to the strength of the electric field formed between the charge accumulating portion and the reading light side electrode layer. When the amount of the recording electromagnetic wave is reduced in order to reduce irradiation dose to the patients, the charge of the latent image polarity accumulated in the charge accumulating portion is reduced and the electric field formed between the charge accumulating portion and the reading light side electrode layer becomes weak, which results in poor charged pair generating efficiency and deterioration in sensitivity of the image recording medium to the reading light. Increase of the amount of reading light in order to compensate for deterioration in sensitivity of the image recording medium to the reading light gives rise to a problem of increase in the cost or the like.
In view of the foregoing observations and description, the primary object of the present invention is to provide an image recording medium provided with a photoconductive layer containing therein a-Se as a major component which is free from the problem of bulk crystallization and accordingly is relatively free from the limitation in working temperature and service life.
Another object of the present invention is to provide an image recording medium in which interfacial crystallization due to deposition of the recording light side electrode layer onto the recording photoconductive layer can be suppressed, thereby suppressing the problem of deterioration of the S/N ratio.
Still another object of the present invention is to provide an image recording medium which is high in sensitivity to the reading light.
Still another object of the present invention is to provide a method of manufacturing such an image recording medium.
In accordance with a first aspect of the present invention, there is provided an image recording medium comprising a support permeable to a reading electromagnetic wave and a first electrode layer (a reading light side electrode layer) permeable to the reading electromagnetic wave, a reading photoconductive layer which exhibits conductivity upon exposure to the reading electromagnetic wave, a charge accumulating portion which accumulates an electric charge of a latent image polarity generated in a recording photoconductive layer, the recording photoconductive layer which exhibits conductivity upon exposure to a recording electromagnetic wave and a second electrode layer (a recording light side electrode layer) permeable to the recording electromagnetic wave which are superposed on the support one on another in this order, at least one of the recording photoconductive layer and the reading photoconductive layer being formed of a material containing a-Se as a major component and doped with a material for suppressing bulk crystallization of a-Se.
When both the recording photoconductive layer and the reading photoconductive layer are formed of a material containing a-Se as a major component, it is preferred that both the recording photoconductive layer and the reading photoconductive layer be doped with a material for suppressing bulk crystallization of a-Se.
It is preferred in view of high dark resistance that the recording photoconductive layer be about 50 to 1000 xcexcm in thickness and the reading photoconductive layer be about 0.05 to 0.5 xcexcm in thickness. When the charge accumulating portion is formed by providing a charge transfer layer between the recording photoconductive layer and the reading photoconductive layer, the charge transfer layer may be in the form of a layer of PVK or TPD 0.1 to 1 xcexcm thick and the reading photoconductive layer may be a layer of a-Se 5 to 30 xcexcm thick.
As the material for suppressing bulk crystallization of a-Se, for instance, As (arsenic) is preferred and the doping amount of As is preferably 0.1 to 0.5 atom % and more preferably 0.33 atom %. Doping a-Se with a large amount of As is attended by adverse effect that positive hole traps are increased and the photoconductive layer deteriorates in its inherent function, especially carrier mobility. Accordingly, the doping amount of As should be limited within such a range that the inherent function of the photoconductive layer is not greatly deteriorated.
In order to prevent the adverse effect of doping a-Se with As, it is preferred that the photoconductive layer doped with As be further doped with, for instance, Cl (chlorine), and the doping amount of Cl is preferably 10 to 50 ppm (on the atomic base, the same in the following). More preferably, the doping amount of As is 0.33 atom % and the doping amount of Cl is 30 to 40 ppm.
The image recording medium in accordance with the first aspect of the present invention may be provided with one or more other layers interposed between the aforesaid layers so long as the aforesaid layers are superposed in the aforesaid order.
In accordance with a second aspect of the present invention, there is provided an image recording medium comprising a support permeable to a reading electromagnetic wave and a first electrode layer (a reading light side electrode layer) permeable to the reading electromagnetic wave, a reading photoconductive layer which exhibits conductivity upon exposure to the reading electromagnetic wave, a charge transfer layer which behaves like a substantially insulating material to an electric charge of a latent image polarity generated in a recording photoconductive layer and behaves like a substantially conductive material to the electric charge of the polarity opposite to the latent image polarity, the recording photoconductive layer which exhibits conductivity upon exposure to a recording electromagnetic wave and a second electrode layer (a recording light side electrode layer) permeable to the recording electromagnetic wave which are superposed on the support one on another in this order, the charge transfer layer being formed of a material containing a-Se as a major component and doped with a material for suppressing bulk crystallization of a-Se.
It is preferred that provision be made not to rob the charge transfer layer of its function by said doping. For example, the charge transfer layer is preferably formed of a material containing therein a-Se as a major component and doped with As in 0.1 to 0.5 atom % and Cl in 20 to 250 ppm.
When based on a charge transfer layer formed of a material containing a-Se as a major component and doped with 10 to 200 ppm of Cl, positive hole traps are increased and the function of the charge transfer layer is deteriorated or lost by simply doping the charge transfer layer with As. Accordingly, in order to prevent the adverse effect of doping a-Se with As, the doping amount of As is limited to 0.1 to 0.5 atom % and the doping amount of Cl is limited to 20 to 250 ppm.
The image recording medium in accordance with the second aspect of the present invention may be provided with one or more other layers interposed between the aforesaid layers so long as the aforesaid layers are superposed in the aforesaid order.
In the image recording medium of the second aspect, based on a charge transfer layer formed of a material containing a-Se as a major component and doped with 10 to 200 ppm of Cl, it is preferred that the doping amount of As be 0.33 atom % and the doping amount of Cl be 30 to 40 ppm.
Further, in the image recording medium in accordance with the first or second aspect of the present invention, the thickness of the recording photoconductive layer is preferably 400 to 1000 xcexcm and more preferably 700 to 1000 xcexcm.
In accordance with a third aspect of the present invention, there is provided a method of manufacturing an image recording medium comprising a support permeable to a reading electromagnetic wave and a first electrode layer permeable to the reading electromagnetic wave, a reading photoconductive layer which exhibits conductivity upon exposure to the reading electromagnetic wave, a charge accumulating portion which accumulates an electric charge of a latent image polarity generated in a recording photoconductive layer, the recording photoconductive layer which exhibits conductivity upon exposure to a recording electromagnetic wave and a second electrode layer permeable to the recording electromagnetic wave which are superposed on the support one on another in this order, the method characterized in that
the recording photoconductive layer is formed in a thickness of 200 to 1000 xcexcmm by resistance heating deposition of an alloy material containing therein Se as a major component and doped with 0.1 to 0.5 atom % of As and 10 to 50 ppm of Cl.
In accordance with a fourth aspect of the present invention, there is provided a method of manufacturing an image recording medium comprising a support permeable to a reading electromagnetic wave and a first electrode layer permeable to the reading electromagnetic wave, a reading photoconductive layer which exhibits conductivity upon exposure to the reading electromagnetic wave, a charge transfer layer which behaves like a substantially insulating material to an electric charge of a latent image polarity generated in a recording photoconductive layer and behaves like a substantially conductive material to the electric charge of the polarity opposite to the latent image polarity, the recording photoconductive layer which exhibits conductivity upon exposure to a recording electromagnetic wave and a second electrode layer permeable to the recording electromagnetic wave which are superposed on the support one on another in this order, the method characterized in that
the recording photoconductive layer is formed in a thickness of 200 to 1000 xcexcm by resistance heating deposition of an alloy material containing therein Se as a major component and doped with 0.1 to 0.5 atom % of As and 10 to 50 ppm of Cl.
The reason why the recording photoconductive layer is formed by resistance heating deposition of an alloy material containing therein Se as a major component and doped with 0.1 to 0.5 atom % of As and 10 to 50 ppm of Cl is to make higher the As concentration at the extreme surface of the recording photoconductive layer facing the interface between the second electrode layer (the recording light side electrode layer) and the recording photoconductive layer than that inside the bulk by use of effect of fractional distillation during the resistance heating deposition. In order to obtain such an effect of fractional distillation, the resistance heating deposition in which deposition can be effected at a relatively low temperature is more suitable as compared with other deposition methods such as electron beam deposition, sputtering, and the like.
The recording photoconductive layer may be formed in a thickness of 400 to 1000 xcexcm or 700 to 1000 xcexcm.
In accordance with the first aspect of the present invention, since the recording photoconductive layer and/or the reading photoconductive layer is formed of a material containing a-Se as a major component, the image recording medium can be high in dark resistance, which results in a high S/N ratio. However, when the photoconductive layer is formed of pure a-Se material, the aforesaid problem bulk crystallization occurs. The material for suppressing bulk crystallization of a-Se slows down progress of bulk crystallization and the limitation in working temperature and service life can be relaxed.
Accordingly, the image recording medium in accordance with the first aspect of the present invention can be high in S/N ratio, can withstand a relatively high temperature and is long in service life.
Doping a-Se with a material for suppressing bulk crystallization of a-Se, e.g., As, is attended by adverse effect on inherent function of the photoconductive layer as described above. However the adverse effect can be compensated for by doping with, for instance, Cl together with the material for suppressing bulk crystallization of a-Se, e.g., As.
In accordance with the second aspect of the present invention, since the charge transfer layer is formed of a material containing a-Se as a major component and doped with a material for suppressing bulk crystallization of a-Se, progress of bulk crystallization is slowed down. Accordingly, the image recording medium in accordance with the second aspect of the present invention can withstand a relatively high temperature and is long in service life.
For example, when based on a charge transfer layer formed of a material containing a-Se as a major component and doped with 10 to 200 ppm of Cl, the charge transfer layer is doped with a predetermined amount of As and a predetermined amount of Cl, progress of bulk crystallization can be slowed down without deteriorating the function of the charge transfer layer.
In accordance with the methods of the third and fourth aspects of the present invention, since the recording photoconductive layer is formed by resistance heating deposition of an alloy material containing therein Se as a major component and doped with 0.1 to 0.5 atom % of As and 10 to 50 ppm of Cl, the As concentration at the extreme surface of the recording photoconductive layer facing the interface between the second electrode layer and the recording photoconductive layer is made higher than that inside the bulk as a result of fractional distillation of As and Cl during the resistance heating deposition. As a result, interfacial crystallization due to deposition of the second electrode layer onto the recording photoconductive layer is prevented, and deterioration in S/N ratio due to direct injection of an electric charge from the electrode caused by the interfacial crystallization can be prevented. Further, in accordance with our experiment, use of an alloy material containing Se as a major component and doped with 0.35 atom % of As and 20 ppm of Cl resulted in better interfacial crystallization prevention than use of an alloy material containing Se as a major component and doped with 1.0 atom % of As. This result means interfacial crystallization prevention by increasing the As concentration can be enhanced by using an alloy material doped with Cl in addition to As.
Further, when the recording photoconductive layer is large in thickness (200 to 1000 xcexcm, preferably 400 to 1000 xcexcm and more preferably 700 to 1000 xcexcm), the resistance heating deposition is carried out taking a long time at a relatively low temperature and the As concentration at the extreme surface of the recording photoconductive layer is more increased by fractional distillation, whereby the interfacial crystallization prevention effect can be enhanced.
In accordance with a fifth aspect of the present invention, there is provided an image recording medium comprising a support permeable to a reading electromagnetic wave and a first electrode layer (a reading light side electrode layer) permeable to the reading electromagnetic wave (may be of a transparent oxide film such as ITO), a reading photoconductive layer which is formed of a material containing a-Se as a major component and exhibits conductivity upon exposure to the reading electromagnetic wave, a charge accumulating portion which accumulates an electric charge of a latent image polarity generated in a recording photoconductive layer, the recording photoconductive layer which exhibits conductivity upon exposure to a recording electromagnetic wave and a second electrode layer (a recording light side electrode layer) permeable to the recording electromagnetic wave which are superposed on the support one on another in this order, wherein between the first electrode layer and the reading photoconductive layer is provided an interfacial crystallization suppressing layer which is permeable to the reading electromagnetic wave and suppresses interfacial crystallization of a-Se.
It is preferred that the interfacial crystallization suppressing layer has, in addition to the function of suppressing interfacial crystallization, functions of blocking an electric charge from being directly injected from the first electrode layer, relieving thermal stress caused by the difference in thermal expansion coefficient between the first electrode and the reading photoconductive layer and firmly bonding the first electrode layer and the reading photoconductive layer in close contact with each other.
In the case where the first electrode layer is in the form of a stripe electrode comprising a plurality of line electrodes arranged in a direction perpendicular to the longitudinal direction of each line electrode, it is preferred that the interfacial crystallization suppressing layer be provided continuously along the upper surface (the surface facing the reading photoconductive layer) and the longitudinal side surfaces of each of the line electrodes.
In order to suppress interfacial crystallization, the interfacial crystallization suppressing layer need not be provided between the line electrodes. However, the interfacial crystallization suppressing layer may be provided also on the upper surface of the substrate between the line electrodes for the purpose of simplicity of manufacture. That is, the portion of the interfacial crystallization suppressing layer formed between the line electrodes during formation of the interfacial crystallization suppressing layer along the upper surface and the side surfaces of each line electrode need not be removed.
It is preferred that the interfacial crystallization suppressing layer be formed of a material which is transparent and elastic and is excellent in function of blocking an electric charge from being directly injected from the first electrode layer. For example, it is preferred that the interfacial crystallization suppressing layer be formed of organic insulating polymer such as polyamide, polyimide, polyester, polyvinyl butyral, polyvinyl pyrrolidone, polyurethane, polymethyl methacrylate or polycarbonate, or an organic film material such as a mixture of an organic binder and a low-molecular organic material.
The interfacial crystallization suppressing layer may generally be in the range of 0.05 to 5 xcexcm in thickness. The thickness of the interfacial crystallization suppressing layer is preferably in the range of 0.1 to 5 xcexcm in order to relieve the thermal stress and in the range of 0.05 to 0.5 xcexcm in order to obtain an excellent blocking function without after image. A good compromise therebetween is 0.1 to 0.5 xcexcm.
The image recording medium in accordance with the fifth aspect of the present invention may be provided with one or more other layers such as charge transfer layer to be described later interposed between the aforesaid layers so long as the aforesaid layers are superposed in the aforesaid order.
In accordance with a sixth aspect of the present invention, there is provided an image recording medium comprising a support permeable to a reading electromagnetic wave and a first electrode layer (a reading light side electrode layer) permeable to the reading electromagnetic wave, a reading photoconductive layer which is formed of a material containing a-Se as a major component and exhibits conductivity upon exposure to the reading electromagnetic wave, a charge accumulating portion which accumulates an electric charge of a latent image polarity generated in a recording photoconductive layer, the recording photoconductive layer which exhibits conductivity upon exposure to a recording electromagnetic wave and a second electrode layer (a recording light side electrode layer) permeable to the recording electromagnetic wave which are superposed on the support one on another in this order, wherein the reading photoconductive layer is doped over the whole or in the surface area facing the first electrode layer with an interfacial crystallization suppressing material which suppresses interfacial crystallization of a-Se.
When the reading photoconductive layer is doped with the interfacial crystallization suppressing material in the surface area, a thin film which suppresses interfacial crystallization of a-Se is formed nearest to the reading electromagnetic wave incident face.
As the interfacial crystallization suppressing material, for instance, As (arsenic) is preferred and the doping amount of As is preferably 0.5 to 40 atom %, and more preferably 5 to 40 atom %. When the doping amount of As is smaller than 0.5 atom %, interfacial crystallization preventing effect is not sufficient, whereas when the doping amount of As is larger than 40 atom %, crystallization other than crystallization of Se, such as As2Se3, becomes apt to occur.
When the thickness of the reading photoconductive layer is in the range of 0.05 to 0.5 xcexcm, the response speed in reading is not greatly affected even if the reading photoconductive layer is doped with As in an amount of 0.5 to 40 atom % over the whole. When the thickness of the reading photoconductive layer exceeds the range, it is preferred that the reading photoconductive layer be doped with As in an amount of 0.5 to 40 atom % only in the surface area facing the first electrode layer.
Increase in the positive hole traps and/or the electron traps by doping with As elongates durability of optical fatigue of the interface caused by pre-exposure as will be described later and sometimes contributes to stabilization of offset noise.
In such a case, the amount of increase in the positive hole traps or the electron traps can be controlled by changing the doping amount of As. Up to about 5 atom %, the positive hole traps increases, as the As concentration further increases, the electron traps becomes prominent, and when the doping amount of As is about 40 atom %, the reading photoconductive layer exhibits properties like a-As2Se3, where the electron traps greatly increases and only the positive holes are movable with the electrons hardly movable. The doping amount As may be selected according to the material of the first electrode layer and/or the material of a blocking layer provided between the first electrode layer and the reading photoconductive layer.
Further, electron traps can be increased by doping with Cl in an amount of 1 to 1000 ppm in addition to As. Positive hole traps can be increased by doping with Na in an amount of 1 to 1000 ppm in place of As. The kind of doping material and/or the amount of the doping material may be selected according to the material of the first electrode layer and/or the material of a blocking layer provided between the first electrode layer and the reading photoconductive layer.
The image recording medium in accordance with the sixth aspect of the present invention may be provided with one or more other layers such as charge transfer layer to be described later interposed between the aforesaid layers so long as the aforesaid layers are superposed in the aforesaid order.
In accordance with a seventh aspect of the present invention, there is provided a method of manufacturing an image recording medium which is provided with an interfacial crystallization suppressing layer and a first electrode layer in the form of a stripe electrode comprising a plurality of line electrodes. The method of the seventh aspect is characterized in that the interfacial crystallization suppressing layer is formed by applying an interfacial crystallization suppressing material in the longitudinal direction of the line electrodes.
The interfacial crystallization suppressing layer may be applied after forming the stripe electrode on a support of glass, organic polymer or the like by dipping, spraying, bar coating, screen coating or the like. Dipping is advantageous in that the interfacial crystallization suppressing layer can be formed by simply dipping the support bearing thereon the stripe electrode in solvent and taking it out from the solvent, and that a large size interfacial crystallization suppressing layer can be formed relatively easily.
In accordance with an eighth aspect of the present invention, there is provided an image recording medium comprising a support permeable to a reading electromagnetic wave and a first electrode layer permeable to the reading electromagnetic wave, a reading photoconductive layer which is formed of a material containing a-Se as a major component and exhibits conductivity upon exposure to the reading electromagnetic wave, a charge accumulating portion which accumulates an electric charge of a latent image polarity generated in a recording photoconductive layer, the recording photoconductive layer which exhibits conductivity upon exposure to a recording electromagnetic wave and a second electrode layer permeable to the recording electromagnetic wave which are superposed on the support one on another in this order, wherein an interfacial crystallization suppressing layer which is permeable to the reading electromagnetic wave, suppresses interfacial crystallization of a-Se, and has a function of blocking the electric charge at which the first conductive layer is electrified from being injected into the reading photoconductive layer is provided between the first electrode layer and the reading photoconductive layer, and the reading photoconductive layer is doped over the whole or in the surface area facing the interfacial crystallization suppressing layer with an interfacial crystallization suppressing material which suppresses interfacial crystallization of a-Se and a material which increases traps for a charge of the polarity opposite to that at which the first electrode layer is electrified and reduces traps for the charge of the same polarity as the polarity at which the first electrode layer is electrified.
The interfacial crystallization suppressing layer suppresses interfacial crystallization of a-Se and at the same time has a function of blocking the electric charge at which the first conductive layer is electrified from being injected into the reading photoconductive layer. That the interfacial crystallization suppressing layer has a function of blocking the electric charge at which the first conductive layer is electrified from being injected into the reading photoconductive layer means, for instance, that the layer prevents the electric charge from moving to a space-charge layer formed on the interface between the reading photoconductive layer and a blocking layer to be described later, thereby stabilizing the space-charge layer.
When the reading photoconductive layer is doped over the whole or in the surface area facing the interfacial crystallization suppressing layer with an interfacial crystallization suppressing material which suppresses interfacial crystallization of a-Se and a material which increases traps for a charge of the polarity opposite to that at which the first electrode layer is electrified and reduces traps for the charge of the same polarity as the polarity at which the first electrode layer is electrified, a negative space-charge layer is formed in the whole reading photoconductive layer or the surface area facing the interfacial crystallization suppressing layer in the case where the first electrode layer is positively electrified and the second electrode layer is negatively electrified, whereas, a positive space-charge layer is formed in the whole reading photoconductive layer or the surface area facing the interfacial crystallization suppressing layer in the case where the first electrode layer is negatively electrified and the second electrode layer is positively electrified.
The interfacial crystallization suppressing material may be As, and the doping amount of As is preferably 3 to 40 atom %.
When the first electrode layer is positively electrified, the material which increases traps for a charge of the polarity opposite to that at which the first electrode layer is electrified and reduces traps for the charge of the same polarity as the polarity at which the first electrode layer is electrified may be Cl and the doping amount of Cl is preferably 1 to 1000 ppm.
Whereas when the first electrode layer is negatively electrified, the material which increases traps for a charge of the polarity opposite to that at which the first electrode layer is electrified and reduces traps for the charge of the same polarity as the polarity at which the first electrode layer is electrified may be Na and the doping amount of Na is preferably 1 to 1000 ppm.
It is preferred that the thickness of the region doped with both the interfacial crystallization suppressing material and the material which increases traps for a charge of the polarity opposite to that at which the first electrode layer is electrified and reduces traps for the charge of the same polarity as the polarity at which the first electrode layer is electrified, that is, the region in which both the materials exist, be 0.01 to 0.1 xcexcm.
It is preferred that the reading electromagnetic wave is 350 to 550 nm in wavelength.
The image recording medium in accordance with the eighth aspect of the present invention may be provided with one or more other layers such as charge transfer layer to be described later interposed between the aforesaid layers so long as the aforesaid layers are superposed in the aforesaid order.
In the image recording medium in accordance with the fifth aspect of the present invention, the interfacial crystallization suppressing layer provided between the first electrode layer and the reading photoconductive layer (may be of, for instance, an organic thin film) prevents a-Se from being in direct contact with material of the electrode such as ITO, whereby chemical change of Se is prevented and interfacial crystallization of Se is prevented. Accordingly, charge injection from the electrode due to interfacial crystallization cannot be increased and the problem of deterioration in S/N can be overcome.
Further, the interfacial crystallization suppressing layer may be provided with functions of blocking an electric charge from being directly injected from the first electrode layer, relieving thermal stress caused by the difference in thermal expansion coefficient between the first electrode and the reading photoconductive layer and firmly bonding the first electrode layer and the reading photoconductive layer in close contact with each other so that deterioration in S/N ratio can be prevented and structural failure such as breakage of the reading photoconductive layer and/or the support and/or peeling from each other due to thermal stress can be prevented.
In the case where the first electrode layer is in the form of a stripe electrode, when each of the line electrodes is covered with the interfacial crystallization suppressing layer continuously along the upper surface and the longitudinal side surfaces thereof, the reading photoconductive layer can be surely prevented from being in contact with the first electrode layer and interfacial crystallization of a-Se can be surely prevented.
Further, by simply applying an interfacial crystallization suppressing material, e.g., an organic polymer material, in the longitudinal direction of the line electrodes, the reading photoconductive layer can be surely kept away from the electrode.
In the image recording medium in accordance with the sixth aspect of the present invention, chemical change of Se at the interface between the reading photoconductive layer and the first electrode layer is prevented and interfacial crystallization of Se is prevented by the interfacial crystallization suppressing material in the reading photoconductive layer, whereby deterioration in S/N ratio due to local change of photoelectric properties of the reading photoconductive layer can be prevented. When the reading photoconductive layer is doped with the interfacial crystallization suppressing material in the surface area, a result substantially equivalent to that obtained when a thin film which suppresses interfacial crystallization of a-Se is formed nearest to the reading electromagnetic wave incident face can be obtained and interfacial crystallization of a-Se in the reading photoconductive layer can be more surely suppressed.
Positive hole traps or electron traps are generally increased at the interface by doping with As, which deteriorates the functions of the photoconductive layer. However, increase in the positive hole traps or the electron traps elongates durability of optical fatigue and sometimes contributes to stabilization of offset noise. The durability of optical fatigue can be adjusted by doping with Cl or Na in an amount of 1 to 1000 ppm in addition to As.
Further, in the image recording medium in accordance with the eighth aspect, a positive or negative space-charge layer is formed in the reading photoconductive layer, which increases the strength of the electric field and the charged pair generating efficiency, thereby increasing the sensitivity to the reading light.
When the reading photoconductive layer is doped with As in an amount of 3 to 40 atom %, the space-charge layer can be formed efficiently without deterioration in inherent functions of the photoconductive layer and the charged pair generating efficiency can be further increased.
When the first electrode layer is positively electrified, and As is employed as the material for suppressing interfacial crystallization of a-Se with 1 to 1000 ppm of Cl or Na used as the material which increases traps for a charge of the polarity opposite to that at which the first electrode layer is electrified and reduces traps for the charge of the same polarity as the polarity at which the first electrode layer is electrified, the positive or negative space-charge layer can be formed more efficiently without deterioration in inherent functions of the photoconductive layer and the charged pair generating efficiency can be further increased.
When the thickness of the region doped with both the interfacial crystallization suppressing material and the material which increases traps for a charge of the polarity opposite to that at which the first electrode layer is electrified and reduces traps for the charge of the same polarity as the polarity at which the first electrode layer is electrified is 0.01 to 0.1 xcexcm, the thickness of the doped region becomes not larger than the depth of reading light absorption of the reading photoconductive layer and the charged pair generating efficiency can be further increased.
Further, when the reading electromagnetic wave is 350 to 550 nm in wavelength, the charged pair generating efficiency can be further increased.